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Home > Technical Library > Fuel Injector Selection

Fuel Injector Selection

Fuel Injector Selection
Make your injected car keep up with hardcore modification using our parts

CAPA can supply an extremely large range of fuel injectors for both performance and standard applications at extremely competitive pricing. We have access to all of the major performance brands of Fuel Injector ranging from Bosch to Rochester. We can supply individual injectors that are capable of flowing up to 120hp! No matter what your project is we have the injectors for it.
Selecting the Right Injector
In order to select the correct size injector for your application, you might wish to use one of the following formulas.

In most cases a naturally aspirated engine will have a B.S.F.C of .50. This means that the engine will use .50 lbs. of fuel per hour for each horsepower it produces. Supercharged engines will want to be at .60 lbs. per hour or higher.

Using these numbers as a guideline, you can select the approximate injector size in the following formula for a four cylinder, naturally aspirated engine at 200 bhp.

Most injectors will max out at 80% duty cycle and this is the accepted industry standard.

B.S.F.C is brake specific fuel consumption - How much fuel you are using per horsepower per hour

Horsepower x B.S.F.C

No. of injectors x .80 
(duty cycle)


200 x .50


= 31.25 lbs. / hr. per inj. x 10.50
= 328 cc / min
The proper injector for this application would be 31 lbs. / hr. or 330 cc / min

To find the HP value of the of the above mentioned injectors use this formula:

Inj. size (in lbs. / hr.), 31.25 x (80% duty) / .50 B.S.F.C = 50 hp. per inj. x 4 inj. = 200hp.

  To convert cc / min to lbs. / hr. - Divide by 10.5

  To convert lbs. / hr to gal. / hr - Divide by 6

  To convert cc / min to gal. / hr. - Multiply by .015873

To find the fuel flow change from a fuel pressure change:



 x Old Flow = New Flow

To convert injector flow rates to horsepower potential - multiply static flow

rates by .80 and then use one of the following formulas:

  To convert cc / min to horsepower - multiply by .190476 x number of injectors

  To convert lbs. / hr. to horseower - multiply by 2 x number of injectors

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